Flexible wood product



. Patented F ebo 29, ran

. errant HEXEIE W001i) PRODUCT William Karl llioughborough, Madison,Wis.; dedicated to the free use of the People in the territory or theUnited States No Drawing. Application January 7, 1942, Serial No.425,867

1 Claim. (@i, IVA-09) (Granted under the act oi ldarch 3, 1883, as

. amended iipril 30, l

. This application is made under the act of March 3,1883, as amended bythe act'of April 39, 3.928, and the invention herein described andclaimed, if patented, may be manufactured and used by or for theGovernment of. the United States of America for governmental purposeswithout the payment to me of any royalty thereon.

I hereby dedicate the invention herein, de-

scribed to the free use 01 the People in, the territory or the UnitedStates to take effect on the granting of a patent-to me. I

My invention relates to processes for rendering dry wood flexible at alltemperatures.

Another object of my invention relates to a secondary treatment, wherebythe wood complex is converted from a product of no elasticity to onehaving a high degree of elasticity.

In my prior Patent No. 2,298,017, datedOctoher 6, 1942, there istaught'that when green southern swamp white oak is impregnated with asuitable amount of urea and then dried to a low moisture content, itbecomes so soft and flexible that it may be very easily-bent, twisted orotherwise deformed when heated to atemperature of about 215 F. It isfurther disclosed that any form given the wood when hot is retained bythe product when cooled to room temperatures. In other words, the ureacomrbines with some or all of the elements of the natural wood to form athermoplastic resin. A a

product that becomes plastic on heating is obviously undesirable forcertain purposes. Hence, efiorts were made to develop a process forresinltying the plastic wood, thus converting the thermoplastic productinto a thermosetting product. This change is brought about by treatingthe compressed urea treated wood with an aldehyde, preferablyformaldehyde, either as an aqueous solution or as ages. This inventionis disclosed in my prior Patent No; 2,313,953, dated March 16, 1943.

The present invention difiers'fromthe above in that the treated wood ofany thickness or length, whether laminated or not, unlike the productdisclosed in Patent No. 2,298,017 is exceedingly flexible, even whencold.

1 am also familiar with another process which renders wood permanentlyplastic by the application of a compression parallel to the grain loadin excess of the elastic limit. My present invention differs from thisprocess, in that the load is applied to the urea treated wood at rightangles to the grain. Moreover, according to the present invention. thewood is not rendered per-- manently plastic., It can be given greaterstrength and stiffness by the secondary aldehyde treatment.

A specific method that may be employed in producing the product coveredby this invention is as follows:

I may soak green sweetgum veneer for two days in an aqueous ureasolution that is saturated at room temperature. It may then be dried toa weight which is in equilibrium with C. and. 40 percent relativehumidity-which would ultimately dry normal Wood to a moisture content of6 percent. The treated sheets, either separately or laminated, areplaced in a female form or chase and subjected to a slight pressurewhile their temperature is raised to about 175 C. when a maximumpressure of substantially 500 pounds per square inch is applied at rightangles to the grain. Before the pressure is finally re-. leased, theproduct is cooled to a temperature of about 60 C. These conditions ofmaximum pressure and temperature are maintained for a period whichvaries with the thickness and species of material being pressed. I havefound that with thicknesses of about one-half inch, about 15 minutes atmaximum temperature and pressure is sufficient to produce a panel whichis surprisingly plastic at all temperatures, even when maintained at'amoisture content that is in equilibrium with normal room atmosphere.

The product treated as above can be curved, or otherwise deformed, andwhile being held to the desired shape, placed in a bath of commercialformaldehyde solution, or a saturated solution of dimethanal urea, ortreated-in formaldehyde in the gaseous state, or treated in any aldehydewhich, in combination with urea, forms a thermosetting resin.

In order to produce my product, via, a resinified sheet wood material,it is first necessary to remove any excess moisture, then heat the ureaaldehyde product to a temperature of about Accordingly, it will be seenthat I may produce (1) a wood product that is flexible at alltemperatures, the flexibility having been brought about by a ureatreatment and by restraining transverse and longitudinal flow whensubjected to a suitable press schedule of temperature and pressure; (2)a process of making wood flexible at all temperatures by first soakingit in a urea solution, drying it, and finally placing it in a suitablefemale form or chase and compressing it to about half of its originalthickness at elevated temperatures, and finally cooling under pressure;(3) a wood product or great strength and stillness produced bysubjecting the flexible wood, as described in (l), to an aldehyde; and(4) a process tor'making the flexible woodprodnot, described in (1),into a product of great strength and stillness;

Having thus described mi invention, what I claim for Letters Patent is:

A process of making wood flexible at all temperatur'es, comprising thesteps or first saturat- 10 in: the wood in an aqueous urea solution atroom 1 temperature; thence drying to awelsht which is in equilibriumwith substantially 60 C. and 40 percent relatirc humidity; thencesubjecting the treated wood in the form of veneer or boardstoatemperat'ure of substantially 175 C. and a pressure of substantially500 pounds per square inch, thence cooling the product to a tempera-

